Flyback converter circuit, flyback switching power supply and power adapter

Abstract

The application discloses a flyback converter circuit, a flyback switching power supply and a power adapter, and relates to the technical field of switching power supplies, which comprises a transformer, a main switch tube, an energy storage inductor, a first diode and a second diode. The first end of the energy storage inductor is connected to a power input end; the anode of the first diode is connected to a common node of a transformer primary winding and the main switch tube, and the cathode of the first diode is connected to the second end of the energy storage inductor; the anode of the second diode is connected to the second end of the energy storage inductor, and the cathode of the second diode is connected to a ground end. When the main switch tube is turned off, the energy in the transformer leakage inductance is transferred through the first diode and stored in the energy storage inductor, effectively clamping the voltage peak on the main switch tube; when the main switch tube is turned on again, the energy in the energy storage inductor is released back to the power input end through the loop formed by the second diode. The application realizes lossless absorption through the capture and reuse of leakage energy, and significantly improves the overall working efficiency of the power supply.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to a flyback converter circuit, a flyback switching power supply, and a power adapter. Background Technology

[0002] Flyback switching power supplies are widely used in small to medium power applications, such as power adapters, chargers, and standby power supplies for household appliances, due to their simple structure, low cost, and good electrical isolation performance. In a typical flyback converter, the transformer not only performs energy transfer and electrical isolation, but also inevitably has leakage inductance during operation. This leakage inductance is caused by the incomplete coupling of the magnetic flux linkages between the primary and secondary windings of the transformer. When the main switching transistor (usually a MOSFET) switches from the on state to the off state, the magnetizing current flowing through the primary winding is quickly cut off. However, since the inductor current cannot change abruptly, the energy stored in the leakage inductance will resonate at a high frequency with the parasitic capacitances such as the junction capacitance of the switching transistor, resulting in a very high voltage spike superimposed on the drain of the switching transistor. This spike voltage is much higher than the sum of the input voltage and the reflected voltage. If not suppressed, it can easily exceed the rated withstand voltage of the switching transistor, causing permanent damage to the switching transistor due to overvoltage, seriously affecting the reliability of the entire power supply.

[0003] To address the aforementioned issues, traditional technologies typically employ passive RCD (resistor-capacitor-diode) snubber circuits. This circuit is usually connected in parallel across the primary winding of the transformer or the main switching transistor. Its working principle is as follows: when the main switching transistor is turned off, the diode transfers leakage inductance energy and stores it in the snubber capacitor, thereby clamping voltage spikes to a safe level. Subsequently, the energy stored in the snubber capacitor is dissipated through the resistor connected in parallel. However, the RCD snubber circuit is inherently a lossy energy processing method. It dissipates usable leakage inductance energy as heat across the resistor, which not only reduces the overall efficiency of the converter but also generates additional heat, increasing the thermal design burden of the system. This deficiency is becoming increasingly apparent in modern power supply designs with increasingly stringent requirements for efficiency and power consumption. Therefore, designing a circuit that can losslessly process leakage inductance energy and effectively suppress voltage spikes while improving power supply efficiency has become a pressing technical problem for those skilled in the art. Utility Model Content

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a flyback converter circuit, a flyback switching power supply, and a power adapter, which can effectively suppress voltage spikes while improving power supply efficiency.

[0005] In a first aspect, embodiments of this application provide a flyback converter circuit.

[0006] A flyback converter circuit according to an embodiment of this application includes: a power input terminal and a ground terminal; a transformer including a primary winding and a secondary winding, wherein a first end of the primary winding is connected to the power input terminal; a main switch transistor, the control terminal of which is used to receive a switching signal, the input terminal of which is connected to the second end of the primary winding, and the output terminal of which is connected to the ground terminal; an energy storage inductor, the first end of which is connected to the input terminal; a first diode, the anode of which is connected to the second end of the primary winding, and the cathode of which is connected to the second end of the energy storage inductor; and a second diode, the anode of which is connected to the second end of the energy storage inductor, and the cathode of which is connected to the ground terminal.

[0007] The flyback converter circuit according to the embodiments of this application has at least the following beneficial effects: The flyback converter circuit of the embodiments provides a highly efficient leakage inductance energy handling scheme by adding a leakage inductance absorption network composed of an energy storage inductor, a first diode, and a second diode. When the main switch is turned off, the voltage spike generated by the leakage inductance of the primary winding is turned on through the first diode, transferring the leakage inductance energy that would otherwise impact the main switch and storing it in the energy storage inductor. This effectively clamps the voltage on the main switch, preventing it from being damaged due to overvoltage, and significantly improving the reliability of the circuit. When the main switch is turned on again, the energy storage inductor releases energy and resets through the loop formed by the second diode, preparing for the next switching cycle. Compared to the traditional method of using an RCD absorption circuit to directly dissipate leakage inductance energy as heat through a resistor, the solution of this application captures and reuses this energy, avoiding direct energy loss and effectively improving the overall operating efficiency of the flyback converter. Furthermore, by reducing the ineffective conversion of energy to heat, the heat generation of the system is also reduced, alleviating the burden of heat dissipation design. This circuit is composed of only passive components, has a simple structure, low cost, is easy to implement, and has high practical value.

[0008] According to some embodiments of this application, an input capacitor is also included, which is connected in parallel between the power input terminal and the ground terminal.

[0009] According to some embodiments of this application, the inductance value of the energy storage inductor is greater than the leakage inductance value of the primary winding.

[0010] According to some embodiments of this application, at least one of the first diode and the second diode is a fast recovery diode.

[0011] According to some embodiments of this application, the secondary winding is connected to a rectifier and filter circuit, which includes a rectifier diode and an output filter capacitor.

[0012] Secondly, embodiments of this application provide a flyback switching power supply, including a flyback converter circuit according to any one of the embodiments of the first aspect.

[0013] Thirdly, embodiments of this application provide a power adapter, including a flyback converter circuit according to any one of the embodiments of the first aspect. Attached Figure Description

[0014] The present application will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of the flyback converter circuit structure according to an embodiment of this application. Detailed Implementation

[0015] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0016] In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0017] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0018] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0019] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0020] In a first aspect, embodiments of this application provide a flyback converter circuit.

[0021] like Figure 1 As shown, the flyback converter circuit of this embodiment includes a power input terminal Vin and a ground terminal GND, a transformer T, a main switch Q1, an energy storage inductor L1, and a first diode D1 and a second diode D2. For example, the transformer T includes a primary winding and a secondary winding, wherein the first end of the primary winding is connected to the power input terminal Vin. The main switch Q1 is preferably a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), whose control terminal (gate) is used to receive a switching signal generated by an external controller (not shown) to control its periodic on and off states. The input terminal of the main switch Q1 is connected to the second end of the primary winding of the transformer T (point C in the figure), and its output terminal is connected to the ground terminal GND.

[0022] The core of the flyback converter circuit in this embodiment lies in a leakage inductance energy recovery network consisting of an energy storage inductor L1, a first diode D1, and a second diode D2. The first terminal (point A) of the energy storage inductor L1 is connected to the power input terminal Vin. The anode of the first diode D1 is connected to the second terminal (point C) of the primary winding of the transformer T, and its cathode is connected to the second terminal (point B) of the energy storage inductor L1. The anode of the second diode D2 is connected to the second terminal (point B) of the energy storage inductor L1, and its cathode is connected to the ground terminal GND.

[0023] During the conduction of the main switch Q1, when the control terminal of Q1 receives a high-level switching signal, Q1 conducts, and its drain and source are approximately closed. At this time, the input voltage Vin forms a current loop through the primary winding of transformer T, point C, and the conducting Q1. The current increases linearly, and energy is stored in the magnetizing inductance of transformer T in the form of a magnetic field. During this stage, the potential at point C is close to GND. Since the first terminal A of the energy storage inductor L1 is connected to Vin, and its second terminal B is connected through the cathode of the first diode D1, and the anode of D1 (point C) is at a low potential, the first diode D1 is in a reverse cutoff state. At the same time, the cathode of the second diode D2 is grounded, and the potential of its anode (point B) is approximately Vin (ignoring the DC voltage drop of L1), so the second diode D2 is also in a reverse cutoff state. At this time, the leakage inductance recovery network is not working.

[0024] At the instant the switching transistor Q1 is turned off, the flyback converter circuit in this embodiment is in the leakage inductance energy recovery stage. When the control terminal of the main switching transistor Q1 receives a low-level switching signal, Q1 quickly switches from the on state to the off state. The current path flowing through the primary winding is suddenly cut off. According to the characteristic that the inductor current cannot change abruptly, the energy stored in the transformer leakage inductance will try to maintain the current flow, thereby generating a high-amplitude induced electromotive force at point C (i.e., the drain of Q1), which is positive at the top and negative at the bottom, forming a voltage spike. This spike voltage will be superimposed on the input voltage Vin. As the voltage at point C rises rapidly, when its voltage exceeds "Vin + instantaneous voltage drop on L1 + forward conduction voltage drop of D1", the anode potential of the first diode D1 is higher than its cathode potential, and D1 will conduct forward. At this time, a new current path is formed: flowing out from point C, passing through the first diode D1 and the energy storage inductor L1 in sequence, and finally converging into the power input terminal Vin. Through this path, the leakage inductance energy of the transformer is rapidly transferred and stored in the energy storage inductor L1. Because the conduction of D1 clamps the voltage at point C near Vin, it effectively suppresses the voltage spike on the drain of Q1, protecting the main switch Q1 from overvoltage damage.

[0025] When the main switch Q1 is turned on again, the flyback converter circuit in this embodiment is in the energy release phase of the energy storage inductor. At the end of a switching cycle, when the main switch Q1 receives the turn-on signal again and turns on, the potential at point C is rapidly pulled down to the GND potential. This causes the anode potential of the first diode D1 to be much lower than its cathode potential (point B has a certain potential at this time due to the energy stored in L1), and D1 immediately turns off in reverse. At the same time, the current of the energy storage inductor L1, which previously stored leakage inductance energy, cannot change abruptly and will seek a new release path. Since Q1 is turned on, the current of L1 flows through point B, the second diode D2, the ground terminal GND, back to the input capacitor C1, and back to terminal A of L1, forming a loop. At this time, the second diode D2 is forward-biased, and the energy stored in the energy storage inductor L1 is released and recovered to the input terminal, replenishing the energy of the input capacitor C1. This process reuses the leakage inductance energy that would otherwise be wasted, thereby improving the energy conversion efficiency of the entire converter. After the energy is released, the second diode D2 naturally turns off, and the entire circuit returns to its initial state, waiting for the next switching cycle.

[0026] In summary, the flyback converter circuit of the embodiment captures leakage inductance energy when Q1 is turned off through D1 and L1, and then releases the energy back to the input terminal through D2 and L1 when Q1 is turned on, forming a complete lossless absorption and energy recovery process, achieving the dual purpose of protecting switching devices and improving circuit efficiency.

[0027] In some embodiments, the flyback converter circuit includes an input capacitor C1, such as Figure 1As shown, the input capacitor C1 is connected in parallel between the power input terminal Vin and the ground terminal GND. First, the input capacitor C1 serves as a filter and energy storage component on the input side. Typically, the input DC power supply contains some AC ripple or noise. The large-capacity input capacitor C1 can effectively filter out this ripple and noise, providing a more stable and smooth DC operating voltage for the entire converter, which is crucial for ensuring the stable operation of the main switch Q1 and the control circuit. Simultaneously, when the main switch Q1 is in the conducting state, the primary winding of the transformer T absorbs a high-frequency pulse current from the input terminal. The input capacitor C1, as a low-impedance local energy source, can instantaneously provide this pulse current, effectively reducing voltage drops caused by line impedance and avoiding impact on the front-end power supply system, thus ensuring the stability of the input voltage. Secondly, the input capacitor C1 plays a key role in receiving and storing recovered energy. As detailed in the aforementioned working principle, when the main switch Q1 is turned on again, the leakage inductance energy previously stored in the energy storage inductor L1 is released through the second diode D2. The released energy forms a current loop that recharges the input capacitor C1 connected in parallel. In other words, the input capacitor C1 serves not only as an input filter for the circuit but also as the direct destination for the energy recovered from leakage inductance. The recovered leakage inductance energy is effectively stored temporarily in C1 and immediately used for energy supply in the next switching cycle. This minimizes the energy recovery path and losses, thereby further improving the overall efficiency of the circuit.

[0028] Understandably, the energy recovery process of the flyback converter circuit in this embodiment is essentially a transfer of energy from the transformer leakage inductance to the energy storage inductor L1. To ensure that the energy stored in the leakage inductance can be fully and smoothly "extracted" and transferred to the energy storage inductor L1 during the extremely short time that the main switch Q1 is turned off, L1 needs to have sufficient "energy holding capacity". In some preferred embodiments, the inductance value of the energy storage inductor L1 is greater than the leakage inductance value of the transformer primary winding. If the inductance value of the energy storage inductor L1 is too small (e.g., less than or equal to the leakage inductance value), during the energy transfer process, the current of L1 will rise rapidly to its peak value, and the voltage across it will also rise sharply, which may cause it to quickly enter a saturation state or fail to absorb all the leakage inductance energy before the voltage spike reaches a dangerous value, thereby weakening the voltage clamping effect on the main switch Q1. Conversely, by selecting an inductor L1 with a larger value than the leakage inductance value, it can be ensured that the energy transfer path takes place under a relatively lower and smoother impedance. This allows the energy storage inductor L1 to absorb current at a controlled rate, ensuring that there is enough time to transfer most of the leakage inductance energy during the entire switching transient process, thereby reliably clamping the voltage spike on the main switch Q1 to a safe level.

[0029] In some preferred embodiments, at least one of the first diode D1 and the second diode D2 is a fast recovery diode or a Schottky diode. Since the flyback converter operates at a high switching frequency, the diodes in the circuit need to switch on and off rapidly. Ordinary rectifier diodes have a long reverse recovery time; that is, when switching from forward conduction to reverse cutoff, it takes some time to clear the internal minority carriers. During this period, the diode allows a brief reverse current to flow, which causes significant switching losses and electromagnetic interference. For the first diode D1, when the main switch Q1 switches from off to on, the potential at point C is rapidly pulled down, and D1 needs to switch quickly from forward conduction to reverse cutoff. If D1 recovers slowly, a reverse recovery current will be generated from point B through D1 to point C, forming an instantaneous shoot-through loss, increasing power consumption and generating heat. For the second diode D2, it also needs to be quickly cut off to block reverse voltage when the energy storage inductor L1 is fully released or Q1 is turned off. Therefore, using fast recovery diodes or Schottky diodes with even faster recovery speeds can significantly shorten their reverse recovery time, making the diode's switching process "cleaner and crisper." This effectively reduces the diode's own switching losses and the additional stress caused to the main switch Q1, which not only further improves the overall efficiency of the circuit but also helps improve the electromagnetic compatibility (EMC) characteristics of the entire power supply.

[0030] Understandably, in some embodiments, a rectifier-filter circuit is connected to the secondary winding of transformer T. For example, a typical structure includes a rectifier diode and an output filter capacitor. For example, the anode of the rectifier diode is connected to one port of the secondary winding of transformer T (e.g., a "non-same-name terminal" designed according to the polarity of the induced voltage), and the cathode of the rectifier diode is connected to the positive terminal of the output voltage; the output filter capacitor is connected in parallel at the output terminal, with its positive terminal connected to the cathode of the rectifier diode and its negative terminal connected to the output common ground. The other port of the secondary winding of transformer T (e.g., its "same-name terminal") is directly connected to the output common ground, thus forming a complete current loop. An external load is also connected in parallel across the output filter capacitor, i.e., between the positive terminal of the output voltage and the output common ground. During the energy transfer phase when the main switch Q1 is turned off: a voltage is induced in the secondary winding of the transformer, the polarity of which causes the anode potential of the rectifier diode to be higher than the cathode potential, thus forward-biasing the rectifier diode. Current flows from the secondary winding, passing through the conducting rectifier diode. This charge the output filter capacitor for energy storage and simultaneously supplies power to the load. The current eventually returns to the other end of the secondary winding via the output common ground. During the energy storage phase when the main switch Q1 is conducting: the polarity of the induced voltage in the transformer secondary winding reverses, causing the anode potential of the rectifier diode to be lower than its cathode potential (the cathode potential is maintained at a positive voltage by the output filter capacitor). The rectifier diode thus experiences reverse voltage and is cut off, blocking the energy path of the secondary winding. During this period, all the energy required by the load is provided by the discharge of the output filter capacitor, thereby maintaining the continuity of the output voltage.

[0031] Secondly, embodiments of this application provide a flyback switching power supply, including a flyback converter circuit according to any one of the embodiments of the first aspect. The principle and beneficial effects of the flyback switching power supply in this embodiment are based on the flyback converter circuit of the first aspect embodiment, and therefore will not be described again.

[0032] Thirdly, embodiments of this application provide a power adapter, including a flyback converter circuit according to any one of the embodiments of the first aspect. The principle and beneficial effects of the power adapter of this embodiment are based on the flyback converter circuit of the first aspect embodiment, and therefore will not be described again.

[0033] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application. Furthermore, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other.

Claims

1. A flyback converter circuit, characterized in that, include: Power input terminal and ground terminal; A transformer includes a primary winding and a secondary winding, wherein the first end of the primary winding is connected to the power input terminal; The main switch transistor has a control terminal for receiving a switching signal, an input terminal connected to the second terminal of the primary winding, and an output terminal connected to the ground terminal. An energy storage inductor, the first end of which is connected to the input terminal; The first diode has its anode connected to the second end of the primary winding and its cathode connected to the second end of the energy storage inductor. The second diode has its anode connected to the second terminal of the energy storage inductor and its cathode connected to the ground terminal.

2. The flyback converter circuit according to claim 1, characterized in that, It also includes an input capacitor, which is connected in parallel between the power input terminal and the ground terminal.

3. The flyback converter circuit according to any one of claims 1-2, characterized in that, The inductance value of the energy storage inductor is greater than the leakage inductance value of the primary winding.

4. The flyback converter circuit according to any one of claims 1-2, characterized in that, At least one of the first diode and the second diode is a fast recovery diode.

5. The flyback converter circuit according to any one of claims 1-2, characterized in that, The secondary winding is connected to a rectifier and filter circuit, which includes a rectifier diode and an output filter capacitor.

6. A flyback switching power supply, characterized in that, Includes the flyback converter circuit as described in any one of claims 1-5.

7. A power adapter, characterized in that, Includes the flyback converter circuit as described in any one of claims 1-5.

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